This invention relates to a process for removing oxygenates from paraffins or paraffin and olefin mixture. This invention is in particular useful in removal of oxygenates from C10 to C15 paraffins or a mixture of paraffins and olefins prior to use of these paraffins or olefins or mixtures thereof in further processes or reactions.
There are a number of industrial applications for paraffins or olefins or mixtures thereof in the C10 to C15 range. Among these uses are as a precursor to linear alkylbenzene benzene (LAB) which is used to produce linear alkylbenzene sulfonate (LAS), the workhorse surfactant of the detergent industry. These paraffins or olefins or mixtures thereof can also be used as precursors to be upgraded to higher value fuels. As concerns over pollution caused by traditional fossil fuels increase and as sources of crude oil decrease, there has been increased interest in other sources of energy. One promising source of energy is the synthetic production of fuels, lubricants and other products from natural gas or coal. The gas to fuels process is often referred to as gas-to-liquids or GTL and is often made by the Fischer-Tropsch process. See for example, U.S. Pat. No. 4,973,453, which is incorporated by reference herein. The linear paraffins and olefins in the C10 to C15 range are of particular value in connection with these processes.
The synthetic production of hydrocarbons by the catalytic reaction of synthesis gas is well known and is generally referred to as the Fischer-Tropsch reaction. The Fischer-Tropsch process was developed in early part of the 20th century in Germany. It was practiced commercially in Germany during World War II and later has been practiced in South Africa.
Synthesis gas (primarily hydrogen and carbon monoxide) is produced from coal or natural gas (methane). Then the synthesis gas is converted to liquid hydrocarbons. The Fischer-Tropsch reaction for converting synthesis gas has been characterized in some instances by the following general reaction:2H2+COcatalyst→—CH2—+H2O.
The hydrocarbon products derived from the Fischer-Tropsch reaction range from some methane to high molecular weight paraffinic waxes containing more than 50 carbon atoms.
Numerous catalysts incorporating active metals, such as iron, cobalt, ruthenium, rhenium, etc. have been used in carrying out the reaction and both saturated and unsaturated hydrocarbons can be produced. The synthesis reaction is very exothermic and temperature sensitive whereby temperature control is required to maintain a desired hydrocarbon product selectivity.
The synthesis gas used in the Fischer-Tropsch reaction may be made from natural gas, gasified coal and other sources. A number of basic methods have been employed for producing the synthesis gas (“syngas”) utilized as feedstock in the Fischer-Tropsch reaction. The numerous methodologies and systems that have been used to prepare synthesis gas include partial oxidation, steam reforming, auto-reforming or autothermal reforming. Both fixed and fluid bed systems have been employed.
The reforming reactions are endothermic and a catalyst containing nickel is often utilized. Partial oxidation (non-catalytic or catalytic) involves sub-stoichiometric combustion of light hydrocarbons such as methane to produce the synthesis gas. The partial oxidation reaction is typically carried out commercially using high purity oxygen.
In some situations these synthesis gas production methods may be combined to form another method. A combination of partial oxidation and steam reforming, known as autothermal reforming, wherein air may be used as the oxygen-containing gas for the partial oxidation reaction has also been used for producing synthesis gas heretofore. Autothermal reforming, the combination of partial oxidation and steam reforming, allows the exothermic heat of the partial oxidation to supply the necessary heat for the endothermic steam reforming reaction. The autothermal reforming process can be carried out in a relatively inexpensive refractory lined carbon steel vessel whereby a relatively lower cost is typically involved.
The Fischer-Tropsch process to produce paraffins and paraffin/olefin mixtures also produces a wide variety of oxygenates. These oxygenates, which include aldehydes, acids, ketones and alcohols, are detrimental in a variety of applications of these paraffins or olefins or mixtures thereof. In particular, the catalysts used to further process the paraffins and paraffin/olefin mixture to their desired end product are poisoned by oxygenates. The oxygenate content needs to be reduced from amounts on the order of about 200 to 400 parts per million in an untreated paraffin/and (or) olefins stream, down to as low as 1 part per million or lower in order for the paraffins or olefins or mixtures thereof to be processed without poisoning the adsorbent/catalyst or otherwise being detrimental in the processing of these paraffins or olefins or mixtures thereof.
There have been several different adsorption schemes proposed for removal of oxygenates from low carbon paraffins, i.e. those averaging about C5. For example, in U.S. Pat. No. 6,111,162, hydrocarbons with 3 to 8 carbon atoms were treated by removal of oxygenated contaminants by an adsorbent comprising silica gel. In U.S. Pat. No. 5,427,689, a variety of polar substances, including water, alcohols, ethers, aldehydes, ketones, amines, mercaptans, organic sulfides and carboxylic acids were removed from a hydrocarbon containing 1 to 10 carbon atoms using a sorbent composition comprising aluminum borate and zirconium borate. However, heretofore, there has not been proposed a process for sufficiently removing oxygenates from the high carbon (C10 to C15) paraffins and paraffin/olefin mixture employed in the process of the present invention. These mixtures comprise from 0 to 50 wt-% olefins and 50 to 99.99 wt-% paraffins. There are often dozens of different oxygenate compounds found in a paraffin and paraffin/olefin mixture feed made by the Fisher-Tropsch process and it is necessary to have a general process that works to remove all the oxygenate species in order to make use of the paraffins and paraffin/olefin mixture in a wide variety of processes. Accordingly, it is the combined presence of these compounds that it is considered desirable to remove from the paraffin and paraffin/olefin mixture feed. In addition, in many applications of the present invention, it is desirable to be able to regenerate the adsorbents used to remove oxygenates from the paraffin and paraffin/olefin mixture feed. There are considerable cost savings in being able to reuse the adsorbents after regeneration of the bed, rather than frequent bed replacement.